All polymers used for implant devices that contact blood are thrombogenic, and no current surface treatments are satisfactory. This project proposes to use a recently characterized peptide,, hirudin, to develop a superior antithrombin surface treatment. Hirudin is one of the most potent antithrombin agents known. It acts by binding tenaciously to thrombin and inhibiting both major thrombin activities: 1) platelet activation, and 2) proteolytic activities that lead to fibrin coagulation. BSI's proprietary immobilization technology will be used to covalently immobilize hirudin onto silicone rubber and polyurethane. Then the hirudin- coated polymers will be assayed for thrombin-binding activity, proteolytic activity of bound thrombin, and platelet adhesion. Phase II studies will compared heparin to hirudin as antithrombin surface treatments and will evaluate the efficacy of these treatments in ex vivo shunt and in vivo blood compatibility assays. Successful completion of this project is expected to produce superior antithrombin surface treatments for devices that are placed in intimate contact with blood.